The present invention relates to electro-mechanical brake device. More particularly, the present invention relates to an electro-mechanical brake device that enables it to sustain braking force in a power-off condition and can realize a parking brake in a power-off condition, that is, a parking mode.
Generally, a brake device of a vehicle decelerates or stops a running vehicle, and further it is a braking device that enables the vehicle to be a parking condition.
In general, there is a friction type of a brake device that transforms a moving energy to heat energy that is radiated to the atmosphere, wherein hydraulic pressure presses a pair of brake pads of both sides toward a brake disk that rotates with a wheel to make it perform a braking function.
However, because the hydraulic type brake device uses a hydraulic pressure that presses brake pads toward a disk side, and therefore there is a drawback that a device configuration is complicated.
That is to say, a conventional hydraulic type brake device needs a master cylinder that is operated by a booster that increases a pedal operation force to generated hydraulic pressure, and a hydraulic pressure line that is connected to a wheel cylinder as well as various complicated devices that controls and assists them, and thus there is a weakness that a predetermined limitation exists on improving reliability and stability of braking performance from the crowdedness and the hydraulic usage.
Recently, due to the above problem, an electro-mechanical brake device (EMB) has been being mainly used to pursue a simplification of a device configuration that a conventional hydraulic type brake cannot have and can improve braking performance reliability and can realize a parking brake function.
The said electro-mechanical brake device uses a motor as a power source, uses a gear speed reducer to amplify torque of the motor, and includes a structure that transforms a rotation movement to a line motion by using a ball screw, and so on.
An electro parking brake (EPB) function is necessary for a parking brake of the electro-mechanical brake device (EMB), and a structure such as a solenoid and a ratchet is mainly used to realize the electro parking brake (EPB) function, due to a characteristic that using a power transmission device such as a ball-screw that power transmission efficiency is high and a friction coefficient is low to realize a braking.
As a conventional art having the above structure, Patent Laid-Open Publication No. 10-2010-0030285 (2010 Mar. 18) is disclosed, in particularly, an electro-mechanical brake (EMB) presses a brake pad more than a press force that is necessary for a parking brake and a power of a solenoid is turned on or turned off, and an instrument of a ratchet shape is operated to maintain the braking force.
However, the conventional art has to a size larger than a conventional hydraulic type caliper, because of this, the size and the weight of an electro-mechanical brake device becomes more larger, a solenoid, a latch and a gear are used together with a gear inside a gear reducer, thus there is a drawback that the structure configuration becomes complicated and the volume thereof becomes larger, and further there is a problem in an aspect of an assembly characteristics and vehicle packaging layout.
Meanwhile, there is a push type and a pull type in a solenoid, and the type is divided by conditions that an operation direction is push direction and an operation direction is pull direction when a power is turned on. When a push type is applied to a parking brake mechanism, a solenoid power is continuously maintained during a parking brake condition to have a vehicle battery exhausted.
On the contrary, when a pull type is applied to a parking brake mechanism, a solenoid power is continuously maintained during a running condition to have a parking brake condition.
In this condition, when a solenoid is turned off by a condition that cannot be predicted such as short cut of a power line of a vehicle, the solenoid is moved to an opposite direction by a compression spring, and there is a danger that a ratchet or an operating portion can be damaged.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.